Sensor with improved gain-setting capability

ABSTRACT

A method of calibrating a sensor such as a photodetector, and device capable of employing that method, are disclosed. The method includes shining light upon a photosensitive device of the photodetector, receiving a first signal from an operator, and increasing a gain of the photodetector. The method also includes discontinuing the shining of the light upon the photosensitive device after the gain has been increased, receiving a second signal from an operator, and decreasing the gain so that the gain is not excessive.

FIELD OF THE INVENTION

The present invention relates to sensors and, more particularly, relatesto circuits that process and amplify incoming signals such as pulsesignals received from sensing devices.

BACKGROUND OF THE INVENTION

A variety of types of sensors exist for application in a wide variety ofsituations. Among these sensors are, for example,photodetectors/photosensors, infrared sensors, laser sensors, microwavesensors, proximity sensors, ultrasonic sensors, inductive sensors,magnetic sensors, among others. Many of these sensors operate bysensing/receiving analog signal inputs. The sensors in turn typicallyprocess these analog signal inputs in various ways.

In particular with respect to photodetectors, for example, such devicesare employed in a wide variety of applications for a wide variety ofpurposes. In some embodiments, a light signal is provided by a lightemitting device at one position and a photodetector is employed atanother position to detect whether that light signal has beeninterrupted or not, either because the light signal is being turned onand off or because something has cut or interrupted the light pathbetween the light emitting device and the photosensitive device.Photodetectors implemented in this manner can be utilized in a varietyof applications such as industrial conveyor systems, in which ittypically is necessary to detect whether items being conveyed havepassed into or left a given region along the conveyor system, or inindustrial systems that are designed to determine whether particularconditions are or are not met (e.g., light curtains).

In many applications, information is conveyed from a light emittingdevice to a photodetector by rapidly switching or pulsing the lightemitting device on and off so. Depending upon the circumstance, thispulsed signal can take the form of a square wave, the form of an AC (oreffectively-AC) signal, or some other form. Based upon the frequency ofthe pulsing, the duration of the pulses, the magnitude of the pulses,the duty cycle, and a variety of other factors (e.g., possibly, thecolor of the light being transmitted), a variety of information can betransmitted to the photodetector. The coding of this information caninvolve, for example, amplitude-modulation, frequency-modulation,phase-modulation, polarity-modulation.

Due to the many uses of photodetector circuits, such circuits havebecome ubiquitous. To reduce the circuits' size and cost, the circuitshave increasingly been implemented in the form of integrated circuitsrather than out of discrete components. Despite such size and costimprovements, however, conventional photodetector circuits neverthelesssuffer from certain inadequacies. First, to the extent that the pulsedor AC information received by the photodetector contains informationthat is of interest, it is necessary that the AC information berecoverable. Yet conventional recovery circuits, such as conventionalrectification or peak detection circuits, typically utilize diodes ortransistors that have significant forward-conductive voltage drops(e.g., 0.7 Volts) across them. Consequently, the resulting signalsoutput by those recovery circuits include an undesirable offset.Further, to the extent that such recovery circuits provide an outputsignal that represents both the positive (e.g., positive with respect toa neutral level of the AC signal) and the negative (e.g., negative withrespect to the neutral level) swings of the received signal,discontinuities are created at the cross-over points between thepositive and negative portions of the output signal as a result of theforward-conductive voltage drops.

Additionally, regardless of the aforementioned issues relating to theforward-conductive voltage drops within recovery circuits, conventionalphotodetectors have additional inadequacies. In particular, it is commonthat the AC signals received by photodetectors include a DC offset. Thisoffset, which can be magnified during propagation within thephotodetector circuit, can significantly distort the resulting outputsignal. Although some conventional photodetector circuits employ DCoffset removal circuitry to address this problem, conventional removalcircuitry typically involves the use of bypassing or decouplingcapacitors that are too large for practical implementation on integratedcircuits. Consequently, conventional photodetector circuits having DCoffset removal circuitry, when implemented on integrated circuits,typically require discrete capacitors coupled to the integratedcircuits. The use of these discrete capacitors increases manufacturingcosts and can impact robustness.

Further, to the extent that any DC offset may have been introduced intothe signal received by the photodetector circuit itself rather thanintroduced as part of the input to the photodetector circuit,conventional DC offset removal circuitry fails to eliminate such DCoffsets. Thus, even though conventional DC offset removal circuitry doesameliorate the DC offset problem (albeit through the use of discretecapacitors), such conventional circuitry cannot by its nature eliminateall DC offsets.

Still another disadvantage associated with conventional photodetectorcircuits generally is that it can be relatively difficult in practicefor technicians to calibrate the circuits. Photodetector circuitscommonly are implemented in situations where it is important that thecircuits be capable of differentiating between high and low levels oflight corresponding effectively to “on” or “off”. During setup of thephotodetector circuits, the circuits are exposed to levels of lightintended to be representative of levels that are likely to beexperienced in practice, and the gain or amplification of the circuitsis then adjusted/calibrated so as to arrive at an output signal that isrepresentative of the light exposure. The calibration process shouldresult in an amplification level that provides a strong output signalbut at the same time does not excessively exaggerate unwanted signalcomponents, particularly noise.

A common conventional practice for conducting this calibration is for atechnician to hold down a button for a specific period of time duringthe calibration process to, where the period of time determines theeventual amount of gain. For example, by holding down the button for anamount of time lower than a threshold, the amplification might be set toone level and, by holding down the button for an amount of time higherthan the threshold, the amplification might be set to a second,different level. While this procedure has been used in practice, theprocedure has proven to be somewhat unreliable, since the amount of gainis dependent upon the skill of the technician performing the adjustment,for example, upon the ability of the technician to hold down the buttonfor an appropriate amount of time. As a result, it is sometimes if notoften difficult to achieve consistency in the calibration ofphotodetectors, particularly insofar as calibrations can be performeddifferently by different technicians.

In view of the above, it would be advantageous if a new photodetectorcould be developed that addressed one or more of the inadequaciesassociated with conventional photodetectors. In particular, it would beadvantageous if a new photodetector circuit could have an AC recoverycircuit that successfully recovered AC information from an introducedsignal without introducing significant distortions into that informationdue to diode-type voltage drops within the AC recovery circuit. It alsowould be advantageous if a new photodetector circuit could be designedthat was capable of lessening or entirely eliminating DC offsetsintroduced to the photodetector circuit in the signals input thereto,where such DC offset removal circuitry could be more easily implementedon integrated circuits without the use of large, discrete capacitorcomponents. It further would be advantageous if such DC offset removalcircuitry not only served to reduce or eliminate DC offsets introducedby the signals input to the photodetector circuits, but also served toreduce or eliminate additional DC offsets introduced by internaloperation of the photodetector circuits themselves. It additionallywould be advantageous if the calibration process of photodetectorcircuits could be improved to reduce the difficulty with whichtechnicians perform the process and improve the repeatability of thecalibration process. It would likewise be advantageous if similardeficiencies to those discussed above with respect to photodetectorsfound in other types of sensors could similarly be ameliorated oreliminated.

BRIEF SUMMARY OF THE INVENTION

The present inventor has recognized the desirability of an improvedphotodetector that would be more easily, reliably, and repeatablycalibrated in terms of its amplifier gain levels than conventionalphotodetectors. The present inventor has further realized thatcalibration of a photodetector need not involve adjusting the amount ofgain based upon the length of time that an operator/technician provideda given signal, but can instead be achieved simply by receiving signalsfrom the operator/technician as to when the photodetector is beingexposed to maximum and minimum lighting conditions and thenautomatically adjusting the gain based upon the light intensity inputsignals received under those conditions. While the present invention insome embodiments relates to the calibration of the gain ofphotodetectors, the present inventor further has recognized that theeasy, reliable, and/or repeatable adjustment of characteristics inaccordance with some or all of the procedures discussed herein are alsoapplicable to other sensor devices and other non-sensor devices inrelation to the adjustment/calibration/setting of the gain of thosedevices as well as possibly other characteristics of those devices aswell.

More particularly, the present invention relates to a method of settingan operational characteristic of a sensor. The method includes exposingthe sensor to a first sensory condition, receiving a first signal fromat least one of an operator and a control device, and adjusting acharacteristic of the sensor in a first manner. The method furtherincludes exposing the sensor to a second sensory condition after thecharacteristic has been adjusted in the first manner, receiving a secondsignal from at least one of the operator and the control device, andadjusting the characteristic in a second manner in at least onecircumstance.

Additionally, the present invention relates to a method of calibrating aphotodetector. The method includes shining light upon a photosensitivedevice of the photodetector, receiving a first signal from an operator,and adjusting a gain of the photodetector in a first direction. Themethod additionally includes discontinuing the shining of the light uponthe photosensitive device after the gain has been adjusted in the firstdirection, receiving a second signal from an operator, and adjusting thegain in a second direction so that the gain meets a desired condition.

Additionally, the present invention relates to a photodetector thatincludes a photosensitive device, and at least one input device by whichit is possible for an operator to provide input signals to thephotodetector. Further, the photodetector includes a variable-gainamplifier circuit coupled to the photosensitive device and capable ofreceiving signals from the photosensitive device indicative of anintensity of light received by the photosensitive device, and a controlcomponent coupled to the variable-gain amplifier circuit and the atleast one input device, wherein the control component provides signalsgoverning the gain of the variable-gain amplifier circuit. The gain ofthe variable-gain amplifier circuit is set in response to two inputsignals provided at the at least one input device, wherein the gain isincreased after one of the two input signals is provided and the gain isdecreased after the other of the two input signals is provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an exemplary photodetector;

FIG. 2 shows two exemplary sections of a modular conveyor system thateach employ the exemplary photodetector of FIG. 1 in one exemplaryapplication of that photodetector;

FIG. 3 shows an exemplary photodetector circuit that is capable ofrecovering AC information from a received input signal, and that can beimplemented in the photodetector of FIG. 1;

FIG. 4 shows an exemplary waveform showing that positive and negativeportions of the recovered AC information in the photodetector circuit ofFIG. 3 have aligned cross-over points so as to avoid significantdiscontinuities in the overall output signal;

FIG. 5 shows an additional exemplary photodetector circuit similar tothat of FIG. 3 except insofar as the photodetector circuit of FIG. 4also includes DC offset removal circuitry;

FIG. 6 shows steps of an exemplary calibration process capable of beingimplemented on certain embodiments of the photodetector circuits ofFIGS. 1–3 and 5; and

FIG. 7 shows steps of an additional exemplary procedure capable of beingimplemented on certain embodiments of the photodetector circuits ofFIGS. 1–3 and 5.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1, an exemplary photodetector 10 is shown in schematicform. The photodetector 10 has a housing 12 that supports at least onephotosensitive device 14 such as a photosensitive semiconductor device.Also inside the housing 12 is circuitry 11 as well as possibly a powersupply (not shown). In preferred embodiments, the circuitry 11 isprimarily or exclusively implemented on one or more integrated circuits,for example, application specific integrated circuits (ASICs) or othermicrochips, albeit in other embodiments the circuitry could be formedfrom discrete components as well.

Depending upon the embodiment, the circuitry 11 can perform any of avariety of functions including, for example, control functions relatingto the control and operation of the photosensitive device 12 andprocessing of the signals received therefrom. Also, as discussed infurther detail below, the circuitry 11 is capable of certain signalprocessing functions such as amplification of signals received from thephotosensitive device 12. The portion(s) of the circuitry performingcontrol functions can also control such signal processing functions inparticular.

The photodetector 10 can supply one or more output signals at an outputterminal 16 as well as, in some embodiments, receive input signals atone or more input terminals. For example, the photodetector 10 can asshown in FIG. 1 have one or more buttons such as a gain-set button 15and light/dark (L/D) button 13, which are discussed in more detailbelow. In alternate embodiments, communication of the photodetector 10with operators/technicians and/or outside machines and other entitiescan be achieved by way of wireless communications devices including, forexample, RFID devices.

In the embodiment shown, the photodetector 10 also in particularincludes three light emitting diode outputs that serve as indicatorlights to operators/technicians who may be installing or operating thephotodetector, namely, a “power” LED 17, a “set” LED 18, and an “on” LED19. In alternate embodiments, none of the LEDs 17–19 need be present, orone or more of those LEDs or other LEDs, or other output indicatordevices (e.g., devices capable of providing sounds such as “beeps” to anoperator/technician), can be provided.

Turning to FIG. 2, the photodetector 10 of FIG. 1 can be implemented ina variety of situations and in relation to a variety of applications.One exemplary application of the photodetector 10 is in a conveyorsystem 20 such as those commonly employed in industrial/manufacturingenvironments. As shown, the conveyor system 20 includes multipleconveyor sections or modules, such as a first conveyor section 22 and asecond conveyor section 24. Further as shown, the first and secondconveyor sections 22 and 24 respectively include pluralities of rollers26 and 28, respectively, as well as first and second light sources 30and 32, respectively, and also first and second photodetectors 34 and36, respectively (each of which could be the photodetector 10 of FIG.1).

The light sources 30 and 32, each of which has its own photoemission orlight emitting device 38 (e.g., a conventional light bulb or a laser),are capable of being turned on and off in a controlled manner. Indeed,depending upon the embodiment, the intensity of the light emitted by thelight sources 30,32 can be varied continuously and/or controlled in atime-varying manner. For example, the intensity of the light emitted bythe light sources 30,32 could be controlled to take the form of a squarewave, a sine wave, a triangular wave, or a pulsed signal of high,medium, low, or variable duty cycle. Further, depending upon thepresence or absence of one or more objects on the rollers 26, 28 betweenthe respective pairs of light emitting devices 30, 32 and photodetectors 34,36, the paths of light between the light emitting devices38 and the photodetectors 34,36 could be uninterrupted or interrupted,as the case may be.

The conveyor system 20 represented by the pair of conveyor sections22,24 of FIG. 2 is only intended to be exemplary of one application inwhich photodetectors such as the photo detector 10 could be implemented,and it should be understood that such photo detectors could also beemployed in a wide variety of other industrial, residential, security,office, agricultural, construction, and other environments andapplications. For example, the photodetector 10 could be employed inconjunction with a security system where interruption of light to thephotodetector signifies the presence of an intruder, or in conjunctionwith a garage door opener of a residential home where interruption oflight to the photodetector signifies the presence of an obstruction thatmight preclude proper closing of the garage door.

Referring to FIG. 3, a portion of the circuitry 11 of the photodetector10 that is of particular interest is shown in simplified schematic form,as circuitry 40. As discussed further below, the circuitry 40 inparticular serves the purpose of allowing the photodetector 10 toamplify time-varying signals received from the photosensitive device 14.It will be understood to those of ordinary skill in the art thatadditional components for additional purposes can be added to thecircuitry 40 of FIG. 3; nevertheless, the circuitry shown in FIG. 3 isintended to show certain improvements to photodetector circuitry inaccordance with at least some embodiments of the present invention.

As shown in FIG. 3, the circuitry 40 includes a first amplifier 42 thatis capable of receiving input signals from the photosensitive device 14(see FIG. 1). In the embodiment shown, the first amplifier 42 is anoperational amplifier in a shunt configuration that receives currentsignals from the photosensitive device 14. In particular, a firstterminal 44 of the first amplifier 42 receives current from thephotosensitive device 14 and then that current is returned via a second,return terminal 46. An output signal 48 is provided from the firstamplifier 42 based upon the current flow into and out of terminals 44and 46, and this output signal 48 is provided then to a recovery circuit50, which as discussed below is intended to recover or extract all or aportion of the time-varying (or “AC”) component(s) of the output signal48.

As shown, the recovery circuitry 50 includes first and secondcomplementary (or “balanced” or “mirrored”) metal-oxide-semiconductorfield-effect-transistors (MOSFETs) 52 and 54, where the first MOSFET 52is a P-channel MOSFET and the second MOSFET 54 is an N-channel MOSFET.As shown, the output signal 48 is provided to a junction 51 to whicheach of the sources of the first and second MOSFETS 52, 54 is coupled.Additionally, the junction 51 is coupled to an inverting input of asecond amplifier 56 that also is an operational amplifier. As shown, thenon-inverting input of the second amplifier 56 is coupled to a referencevoltage 58 while an output 60 of the second amplifier is coupled to ajunction 62, to which each of the gates of the first and second MOSFETs52,54 is coupled.

Further as shown, the current output from a drain 64 of the secondMOSFET 54 is directed to a ground 66, while the current output from adrain 68 of the first MOSFET 52 is provided to a third MOSFET 70. Thethird MOSFET 70 is part of a current mirror circuit 72 formed by thecombination of that third MOSFET along with a fourth MOSFET 74. Asshown, each of the third and fourth MOSFETs 70,74 is a N-channel MOSFET,and the sources of both MOSFETs are coupled to a supply voltage 76.Also, the gates of the third and fourth MOSFETs 70, 74, are coupled toone another, and also the drain of the third MOSFET is coupled to itsgate. A drain 78 of the fourth MOSFET 74 is coupled to a resistor 80,which is coupled between the drain 78 and the ground 66. The voltageacross the resistor 80, provided at an output terminal 82, constitutesthe output of the circuitry 50. This voltage is determined by thecurrent flowing through the resistor 80, which in turn due to thefunctioning of the current mirror circuit 72 is equal to that of thecurrent flowing out of the drain 68 toward the third MOSFET 70.

The first and second MOSFETs 52 and 54 together with the secondamplifier 56 operate as a current splitter circuit 49. As such, thecurrent flowing with respect to the drain 68 of the first MOSFET 52 isrelated to or representative of the positive portion of the time-varyingoutput signal 48, e.g., the portion of the time-varying output signalthat is above a zero or neutral level of that output signal. Similarly,the current flowing with respect to the drain 64 of the second MOSFET 54is related to or representative of the negative portion of thetime-varying output signal 48, e.g., the portion of the time-varyingoutput signal that is below a zero or neutral level of that outputsignal. The neutral level is not necessarily a zero-voltage (or current)level, but rather typically can be understood as the level at which thearea formed between the positive portion of the time-varying outputsignal and that level would be equal, over time, to the area formedbetween the negative portion of the time-varying output signal and thatlevel.

The recovery circuitry 50 shown in FIG. 3 is specifically configured toprovide the output 82 that is representative of the positive portion(e.g., above the neutral level) of the time-varying output signal 48received from the amplifier 42, but not the negative portion (e.g.,below the neutral level). As such, the recovery circuitry 50 functionssomewhat like a half-wave rectifier, with the information correspondingto the negative portion of the time-varying output signal 48 beingshunted to ground via the drain 64. Half-wave rectification is often ofinterest by itself insofar as, in many applications, only the pulsing onof the light source sending light to the photo detector is of interest,and further because typically the pulsing on of that light sourceoccupies a relatively small proportion of the overall time of operation(e.g., the light transmission is a low duty cycle signal).

Nevertheless, because the first and second MOSFETs 52, 54, arecomplementary, in alternate embodiments a current mirror circuit similarto the current mirror circuit 72 could be coupled to the drain 64 of thesecond MOSFET 54 so as to provide an additional output (not shown)representative of the current flowing with respect to the drain 64,which in turn would be representative of the negative portion of thetime-varying output signal 48. (Such an additional current mirrorcircuit is largely shown in FIG. 5, albeit in that example the secondmirror circuit is not being employed for the purpose of providing anadditional output.) Thus, while the AC recovery circuitry 50 and theembodiment of FIG. 3 operates similarly to a half-wave rectifier insofaras only the positive portion of the time-varying output signal 48received from the amplifier 42 is reflected in the output of thecircuitry 50, the circuitry could readily be modified to operate as afull-wave rectifier.

The recovery circuit 50 shown in FIG. 3 is advantageous in comparisonwith conventional recovery circuitry because it recovers thetime-varying information provided from the amplifier 42 in a manner thatis less distorted than is the case when conventional recovery circuitryis utilized. In particular, through the use of the first and secondMOSFETs 52 and 54, and the second amplifier 56, the output currentprovided by the drain 68 (as well as at the drain 64) is not distorteddue to the introduction of one or more diode-type forward biased voltagedrops (e.g., 0.7 volt). Consequently, the output voltage at outputterminal 82 is more closely reflective of the positive portion of thetime-varying output signal 48 than would be the case if conventionalrecovery circuitry were employed.

Although FIG. 3 shows the use of MOSFETs 52 and 54, othertransistor-type devices could also be employed. For example, in onealternate embodiment the first, P-channel MOSFET 52 could be replacedwith a PNP bipolar junction transistor (BJT), while the second,N-channel MOSFET 54 could be replaced with a NPN BJT. In such anembodiment, the bases of the BJTs would be coupled to the junction 62,while the emitters of the BJTs would be coupled to the junction 51 andthe collectors of the BJTs would provide the output currents similar tothe drains 68,64. In such embodiment, BJTs could also be employed in thecurrent mirror circuit 72 as well. Further, in additional embodiments, avariety of different combinations of MOSFETs, BJTs, and other transistoror switching devices could be employed.

FIG. 4 shows in a graphical manner the advantageous, relativelyundistorted output signals that are provided by the recovery circuitry50 in accordance with the present design. In particular, FIG. 4 showsboth the positive and negative recovered information provided by thecurrent splitter circuit 49. As shown, the recovered positivetime-varying information associated with the drain current at the drain68 of the first MOSFET 52 (I_(d)(M1)) meets up almost continuously withthe negative recovered time-varying information associated with thedrain current at the drain 64 of the second MOSFET 54 (I_(d)(M2)),without any significant discontinuities between the two portions of theinformation at crossover points 65. Thus, were the recovery circuitry 50modified as discussed above to include not only the output terminal 82representative of the positive time-varying information but also anadditional output terminal representative of the negative time-varyinginformation, those two types of information would be fully consistentwith one another.

Referring to FIG. 5, another embodiment of a portion of the circuitry 11of the photodetector 10 relating to amplification of received signals isshown as circuitry 140. Although both circuitry 40 and 140 include thefirst amplifier 42, the circuitry 140 in contrast to the circuitry 40includes somewhat different recovery circuitry 150. As shown, therecovery circuitry 150 like the recovery circuitry 50 receives thetime-varying output signal 48 of the amplifier 42 and processes thatsignal by way of the current splitter circuit 49. Also, similar to therecovery circuitry 50, the recovery circuitry 150 further includes acurrent mirror circuit (in this case labeled circuit 172), thatencompasses both the third MOSFET 70 and the fourth MOSFET 74, thesources of which are coupled to the voltage supply 76. Again, a voltageis output at the output terminal 82 that is representative of thecurrent flowing out of the drain 68 of the first MOSFET 52.

At the same time, the recovery circuitry 150 of FIG. 5 differs from thecircuitry of FIG. 3 insofar as the recovery circuitry 150 includes DCoffset removal circuitry 160 that is coupled to the input 46 of theamplifier 42. The DC offset removal circuitry 160 includes a thirdamplifier 162 (also an operational amplifier) having a noninvertinginput that is coupled to a voltage reference 164, and an inverting inputthat is coupled to a capacitor 166 that in turn is coupled to both theoutput of the third amplifier 162 and to a resistor 168. The resistor168 is coupled between the input 46 of the first amplifier 42 and theoutput of the third amplifier 162, while the capacitor 166 is coupledbetween the inverting input of the amplifier 162 and its output.

In addition to being coupled to the input 46 of the first amplifier 42,the DC offset removal circuitry 160 is also coupled to the remainder ofthe recovery circuitry 150 as follows. As shown, the current mirror 172includes not just the third and fourth MOSFETs 70 and 74, but alsoincludes an additional fifth MOSFET 176 (all three MOSFETs beingn-channel MOSFETs). The fifth MOSFET 176 is coupled with respect to thethird MOSFET 70 and the supply voltage 76 in the same manner as thefourth MOSFET 74, but has a drain 178 that (instead of being coupled toa resistor and providing a voltage output), is coupled to an additionalcurrent mirror circuit 180.

As shown, the additional current mirror circuit 180 parallels thestructure of the third and fifth MOSFETs 70, 176, insofar as it hassixth and seventh MOSFETs 182 and 184 (in this case, p-channel MOSFETs),the sources of which are coupled to the ground 66 and the gates of whichare coupled to one another as well as to the drain 64 of the secondMOSFET 54. Further as shown, the drain of the sixth MOSFET 184 iscoupled specifically to the drain 178 of the fifth MOSFET, 176. Theadditional current mirror circuit 180 thus parallels, in relation to thesecond MOSFET 54, the current mirror circuit formed specifically by thethird and fifth MOSFETs 70, 176 in relation to the first MOSFET 52.

The purpose of the fifth MOSFET 176 and the additional current mirrorcircuit 180 is to allow reassembly of the positive and negative portionsof the time-varying information. A junction 186 in particular links thedrains 178, 184 of the fifth and sixth MOSFETs 176, 184, to allow forthe reassembly of the positive and negative portions of the recoveredtime-varying information that was previously split due to operation ofthe current splitter circuit 49. The junction 186 is coupled as an inputto the DC offset removal circuitry 160, and in particular is coupled tothe inverting input of the third amplifier 162 and is also coupled tothe capacitor 166.

The DC offset removal circuit 160, in the configuration shown in FIG. 5,serves to remove two types of DC offsets that otherwise might beintroduced into the output of the recovery circuit 150. First, the DCoffset removal circuitry 160 removes DC offsets that are provideddirectly to the inputs 44, 46 of the first amplifier 42. For example, ifthe current provided to the input 44 of the amplifier 42 varied between5 microamps and 15 microamps, and had an average value of 10 microamps,the DC offset removal circuitry 160 would tend to remove 10 microamps ofcurrent.

Second, the DC offset removal circuitry 160 serves to remove anyadditional DC offsets that are introduced due to the operation of thecurrent splitter circuit 49, as well as the various current mirrorcircuits 172,180. This is achieved because the input to the DC offsetremoval circuitry 160 is tied to the junction 186 between the currentmirror circuits rather than directly to the output 48 of the firstamplifier. However, in alternate embodiments, the input of the ACrecovery circuit 160 could indeed be coupled directly to the output 48of the amplifier 42, although this is less preferred. In such event, theadditional current mirror circuit 180, as well as the fifth MOSFET 176,would no longer be necessary.

Turning to FIG. 6, steps of an exemplary procedure for calibrating thephotodetector 10 of FIG. 1 are shown in an exemplary flow chart 200. Asshown, after starting at a step 202, the photodetector 10 is presentedwith a light path by a technician or other person setting up thephotodetector system in a step 204. For example, the light emittingdevice 38 of FIG. 2 corresponding to the photodetector might be turnedon (this also presumes that there is no physical blockage in the lightpath between the light emitting device and the photodetector). Once thelight path is presented at the step 204, the technician then presses thegain-set button 15 of the photodetector to indicate that a normal ormaximum level of light is being shined on the photodetector, at a step206. Subsequently, at a step 208, the technician releases the gain-setbutton 15.

The pressing and releasing of the gain-set button 15 at the steps 206and 208 provides the photodetector 10 with an indication that the normalor maximum level of light is being shined upon it. Given this to be thecase, the photodetector 10 next at a step 210 resets its control gain toa minimum level, and further at a step 212 causes the photodetector tochange its indication status by illuminating the “set” LED 18 andturning off the “power” LED 17 (see FIG. 1). Then, at a step 214 thecircuitry 11 within the photodetector circuit 10 automaticallyincrements the gain of the amplifier circuitry (e.g., the gain of thefirst amplifier 42 discussed with reference to FIGS. 3 and 5) until acomparator output level is high. In the present embodiment, the gainpreferably is set to a level of 5 times the input signal (e.g., theinput signal at terminals 44,46), although this is not necessary inother embodiments.

After incrementing the gain to a high level at the step 214, thephotodetector 10 at a step 216 causes the “set” LED 18 to flash in anoticeable manner, for example, at a rate of 6 hertz. When this ishappening, the technician realizes that is appropriate to interrupt/endthe shining of the light upon the photodetector 10 by breaking the lightpath or otherwise, at a step 218. Upon discontinuing the shining of thelight upon the photodetector 10, the technician then at steps 219 and220 respectively presses and releases the gain-set button 15 a secondtime, which results in illumination of the “set” LED 18 at a step 221.Because the light has been discontinued, the signal now received at thephotodetector is indicative of a low light level or a dark light leveland consequently, the output of the photodetector should be at a lowlevel. Nevertheless, in certain circumstances, the output of thephotodetector 10 will not be at a low level despite discontinuing thelight upon the photodetector.

In particular, noise can be at a sufficiently high level such that theamplification provided by the circuitry 11 (especially given that thegain is at a relatively high factor of 5) results in a large outputsignal notwithstanding the absence of light being provided to thephotodetector. To avoid a situation where the photodetector outputs alarge signal despite the absence of light upon the photodetector, at astep 222 in this circumstance (e.g., in a circumstance where the outputsignal exceeds a given threshold) decrements the gain until thecomparator output of the photodetector is sufficiently low. For example,at the step 222, the gain could be reduced by 20% of more. To the extentthat the gain is not excessive, and does not need to be reduced, step222 can be skipped. Finally, at a step 224, the resulting gain-settingis stored in a memory portion of the circuitry 11 (or possibly inanother location as well) and subsequently at a step 226 the “set” LEDis turned off while the “power” LED is turned on, thus signifying theend of the procedure at a step 228 such that the photodetector can nowbe used in practice.

The steps of the procedure shown by the flow chart 200 can beimplemented and practiced on the photodetector 10 in a variety ofmanners and by way of a variety of techniques. In certain embodiments,the procedure is implemented by way of programming on an applicationspecific integrated circuit. Such programming can be implemented throughthe use of state diagrams as well as other programming languages. Theparticular procedure of the flow chart 200 is particularly advantageousin comparison with conventional photodetector systems that require atechnician or other operator to carefully hold down a gain selectingbutton for a specific period of time in order to arrive at a particulargain. In contrast to such systems, the present procedure allows foreffectively automatic setting of the gain that is accomplished with onlytwo pushes of a button by the operator.

Referring to FIG. 7, an additional flow chart 230 is provided showing anadditional exemplary procedure that can be performed by thephotodetector 10. This procedure can be implemented in combination with,or separately from, the procedure shown by the flow chart 200 of FIG. 6.As shown in FIG. 7, after starting at a step 232, a technician or otheroperator will press the light/dark (L/D) button 13 at a step 234 andthen release that button at a step 236. The pressing and releasing ofthe button 13 causes the “set” LED to be turned on and the “power” LEDto be turned off, at a step 240. Then, a toggling of an output state ofthe circuitry 11 occurs at a step 238. After the toggling of state atthe step 238, at a step 242, the setting is stored in memory. Finally,at a step 244, the “set” LED is turned off and the “power” LED is turnedback on, at which point the procedure is ended at a step 246.

The procedure of FIG. 7 can be used to toggle a variety of output states(or other states) of the circuitry 11. For example, in one embodiment, astate of the photodetector 10 can be changed from a light setting to adark setting, or vice versa. When in the light setting, thephotodetector provides an output that is indicative of the degree ofbrightness/intensity of the light or magnitude of the light received bythe photodetector, while when in the opposite state the photodetectorprovides an indication of the darkness or relative absence of lightreceived at the photodetector.

Although the present discussion relates to certain embodiments of thepresent invention shown in FIGS. 1–7, the present invention is notlimited to such embodiments. While the amplification, recovery and DCoffset removal circuitry shown in and described with reference to FIGS.3 and 5, as well as the various procedures shown in and described withreference to FIGS. 6 and 7, are described as being particularly usefulin photodetectors such as the photodetector 10, suchcircuitry/procedures are also applicable to other devices and in othercircumstances and applications as well, where the functions provided bysuch circuitry and such procedures are of use. Indeed, the presentinvention is not intended to be limited to use in photodetectors, butrather is intended to be applicable to a wide variety of sensorsincluding both photodetectors/photosensors as well as, for example,infrared sensors, laser sensors, microwave sensors, proximity sensors,ultrasonic sensors, inductive sensors, magnetic sensors, among others.For example, in at least one such embodiment of the invention, thesensor is a proximity detector that is exposed to first and secondsensory conditions, where the exposing of the sensor to the firstsensory condition involves placement of a target object at a locationproximate to the proximity detector, and the exposing of the sensor tothe second sensory condition involves removal of the target object awayfrom the location and away from the proximity detector. It is inparticular envisioned that the particular circuitry and proceduresdescribed above are applicable to a wide variety of sensors that receivesignal inputs, particularly analog signal inputs, that are to beamplified and/or processed in one or more various manners, and/or thatrequire setting/calibration of their gain characteristics and/or someother operational characteristics.

It is additionally envisioned that one or more aspects of the presentinvention are applicable to such various sensors in a variety of sensorapplications in addition to the industrial conveyor system applicationdiscussed above. For example, sensors in accordance with one or moreaspects of the present invention could be employed in other industrialapplications (e.g., in conjunction with light curtains) as well as inrelation to a variety of other residential, security, office,agricultural, construction, and other environments and applications.Additionally, the present inventive embodiments can readily be combinedwith various other electrical or other technologies in a variety ofapplications such as the conveyor application discussed above as well asmany other applications not necessarily relating to conveyor systems orindustrial/manufacturing systems. As mentioned above, signals to andfrom the circuitry discussed herein, whether or not used in relation tophotodetector devices, can be wirelessly transmitted/received by way ofa variety of devices known in the art including Bluetooth devices andRFID devices. Further, it is envisioned that aspects of the presentinvention could be employed in applications not limited to thoseinvolving sensors. For example, the above-discussed circuitry involvingrecovery of time-varying information and/or DC offset removal could beimplemented in circuits used in motor controllers or motor drives.

Also, it is envisioned that numerous particular aspects of theembodiments of the invention discussed above could be varied dependingupon the circumstance. In particular, the exact circuitry and steps ofthe flow charts shown herein are merely exemplary and can be modified inmyriad ways. For example, while the recovery circuitry 150 of FIG. 5 isdescribed as including the DC offset removal circuitry 160, the recoverycircuitry need not be understood to include such circuitry. Indeed, theDC offset removal circuitry 160 of FIG. 5 and the recovery circuitry 50of FIG. 3 can each be implemented alone as well as in combination withone another as shown in FIG. 5. Also for example, while in FIG. 6 it isshown that the incrementing of the gain occurs prior to the decrementingof the gain, it is also possible that those steps could be reversed intheir relative ordering in alternate embodiments. Further, while FIG. 6shows indications as being provided by the pressing and releasing of apush button, the present invention is intended to encompass embodimentsin which operator indications (or indications from other machine controldevices such as computerized controllers) are provided in other manners.Also, while FIG. 6 relates to calibration of gain, the procedure of FIG.6 could also be employed in relation to the calibration or other settingof other characteristics of sensors or other devices, particularly wheresuch characteristics can be varied along a range.

Further for example, as discussed above, the MOSFETs used in thecircuitry shown herein could be replaced with other transistor orswitching devices (e.g., BJTs) that provided the same or similaradvantages. Also for example, the first amplifier 42 shown, which is acurrent-input device, could be replaced with a voltage-input amplifiersuch as the second and third amplifiers 56,162. In the event that theamplifier 42 was a voltage-input device, the resistor 168 in someembodiments would not be necessary and/or, in certain embodiments thefeedback provided to the amplifier from the DC offset removal circuitrycould be provided via a different input to the amplifier rather than toone or both of the inputs 44,46. Further for example, while the outputsignal provided at the output terminal 82 is shown to be a voltageoutput signal, in other embodiments the output signal would be simplythe current flowing out of the drain 78 of the MOSFET 74 (or comparablecomponent). Additionally, while it is envisioned that the circuitry 11would be implemented in the form of one or more integrated circuits(e.g., an application specific integrated circuits), the circuitry couldalso be implemented in other manners such as by way of discretecomponents or by way of software implemented on a computer ormicroprocessor. Additionally for example, some of the steps of the flowcharts could be eliminated or reordered, and other steps could be addedto the flow charts depending upon the embodiment.

It is specifically intended that the present invention not be limited tothe embodiments and illustrations contained herein, but include modifiedforms of those embodiments including portions of the embodiments andcombinations of elements of different embodiments as come within thescope of the following claims.

1. A method of setting an operational characteristic of a sensor, themethod comprising: exposing the sensor to a first sensory condition;receiving a first signal from at least one of an operator and a controldevice; receiving a first sensor signal from the sensor subsequent tothe receiving of the first signal; adjusting a characteristic of thesensor in a first manner, wherein the characteristic is a gain, andwherein the adjusting in the first manner involves incrementing thegain; exposing the sensor to a second sensory condition after thecharacteristic has been adjusted in the first manner; receiving a secondsignal from at least one of the operator and the control device;receiving a second sensor signal from the sensor subsequent to thereceiving of the second signal; generating an amplified signal basedupon the second sensor signal, the amplified signal being related to thesecond sensor signal by the incremented gain; and adjusting thecharacteristic in a second manner in at least one circumstance, whereinthe adjusting in the second manner involves decrementing the gain,wherein the at least one circumstance occurs when the amplified signalexceeds a threshold.
 2. The method of claim 1, wherein the sensor is aphotodetector, the exposing of the sensor to the first sensory conditioninvolves shining of light from a light source upon a photosensitivedevice of the sensor, and the exposing of the sensor to the secondsensory condition involves discontinuing the shining of the light. 3.The method of claim 1, wherein the sensor is a proximity detector, theexposing of the sensor to the first sensory condition involves placementof a target object at a location proximate to the proximity detector,and the exposing of the sensor to the second sensory condition involvesremoval of the target object away from the location and away from theproximity detector.
 4. A method of calibrating a photodetector, themethod comprising: shining light upon a photosensitive device of thephotodetector; receiving a first signal from an operator; adjusting again of the photodetector in a first direction upon the receiving of thefirst signal; discontinuing the shining of the light upon thephotosensitive device after the gain has been adjusted in the firstdirection; receiving a second signal from the operator; and adjustingthe gain in a second direction upon the receiving of the second signalso that the gain meets a desired condition.
 5. The method of claim 4,wherein the first and second signals are received in response to thepressing and releasing of a button on the photodetector by the operator.6. The method of claim 4, wherein the adjusting of the gain in the firstdirection is an incrementing of the gain, the adjusting of the gain inthe second direction is a decrementing of the gain, and the gain isadjusted in the second direction until the gain is no longer excessiveas determined in relation to a threshold.
 7. The method of claim 6,wherein an indication is provided once the gain has been increased thatit is appropriate for the shining of the light to be discontinued. 8.The method of claim 7, wherein the indication is flashing on and off ofa light-emitting diode on the photodetector, and wherein the gain is setto a minimum level upon initially receiving the first signal prior tothe increasing of the gain.
 9. The method of claim 6, wherein the gainis decreased when an amplified signal generated by the photodetectorwhen the shining of the light has been discontinued exceeds a threshold,and wherein a gain setting is stored in a memory after the gain has beenadjusted.
 10. The method of claim 6, wherein the incrementing of thegain involves an increment to a gain factor of approximately 5, andwherein at least one of the first and second signals is received at thephotodetector by way of a wireless transmission.
 11. The method of claim4, wherein the method is performed in conjunction with installing atleast a portion of a conveyor system having the photodetector
 12. Themethod of claim 4, further comprising: receiving a further input signalfrom the operator; and toggling an operational state of thephotodetector.
 13. The method of claim 12, wherein the operational stateof the photodetector is toggled between a light state in which an outputsignal of the photodetector is indicative of an intensity of the lightreceived at the photosensitive device and a dark state in which theoutput signal is indicative of a degree of absence of the light at thephotosensitive device.
 14. The method of claim 12, wherein an indicationof the operational state of the photodetector after being toggled isstored in a memory device associated with the photodetector, and whereinthe further input signal is received by at least one of the pushing andreleasing of a button on the photodetector, and by way of a wirelesstransmission.
 15. A photodetector comprising: a photosensitive device;at least one input device by which it is possible for an operator toprovide input signals to the photodetector; a variable-gain amplifiercircuit coupled to the photosensitive device and capable of receivingsignals from the photosensitive device indicative of an intensity oflight received by the photosensitive device; and a control componentcoupled to the variable-gain amplifier circuit and the at least oneinput device, wherein the control component provides signals governingthe gain of the variable-gain amplifier circuit, wherein the gain of thevariable-gain amplifier circuit is set in response to two input signalsprovided at the at least one input device, wherein the gain is increasedafter one of the two input signals is provided and the gain is decreasedafter the other of the two input signals is provided, and wherein theone input signal occurs when the photosensitive device is exposed to afirst light input and the other input signal occurs when thephotosensitive device is exposed to a second light input that has anintensity level that is less than that of the first light input.
 16. Thephotodetector of claim 15, wherein the one input signal is provided whenlight is shining upon the photosensitive device and the other inputsignal is provided when the light is not shining upon the photosensitivedevice.
 17. The photodetector of claim 15, wherein the at least oneinput device includes a push button, and each of the two input signalsis provided when the push button is pressed and then released.
 18. Thephotodetector of claim 15, further comprising means for providing anindication, wherein the means for providing the indication provides anindication after the gain has been increased.
 19. The photodetector ofclaim 15, wherein at least one of the control component and thevariable-gain amplifier circuit is formed on an application specificintegrated circuit.
 20. The photodetector of claim 15, wherein the oneinput signal is provided prior to the other input signal.
 21. A sensorsystem comprising: a sensing device configured to provide an outputsignal that varies depending upon an intensity level of an input signalreceived by the sensing device; and an application-specific integratedcircuit (ASIC) including a variable-gain amplifier circuit coupled tothe sensing device and capable of amplifying the output signal from thesensing device according to a gain of the amplifier circuit, wherein thegain of the variable-gain amplifier circuit is determined by way of afirst operation in which the gain is increased to a first level inresponse to the sensing device being exposed to a higher-level inputsignal intensity, and a second operation in which the gain is decreasedto a second level in response to the sensing device being exposed to alower-level input signal intensity, and wherein the second operationoccurs in dependence upon a comparison of an amplified signal with athreshold, and the amplified signal is generated by the variable-gainamplifier circuit based upon both the output signal when the sensingdevice is being exposed to the lower-level input signal intensity andthe gain when increased to the first level.
 22. The system of claim 21,wherein the sensing device is a photosensitive device, wherein thehigher-level input signal intensity is a higher-level light intensity,and wherein the lower-level input signal intensity is a lower-levellight intensity.
 23. The system of claim 22, wherein the first operationonly occurs after a first indication has been received indicating thatthe photosensitive device is being exposed to the higher-level lightintensity, and wherein the second operation only occurs after a secondindication has been received indicating that the photosensitive deviceis being exposed to the lower-level light intensity.